Recent years have seen widespread use of electronic equipment which can be operable by touching its screen with a finger, a pen, or the like. In a known method for detecting a touch position in a display screen, a plurality of optical sensors are provided on a display panel and used to sense a projected or reflected image formed by a finger or suchlike approaching the screen. In another known method, to detect a touch position with high accuracy for any display data, a display device is provided with an infrared backlight for emitting infrared light, and a reflected image formed by infrared light is sensed using optical sensors.
In addition to the infrared backlight, such a display device with optical sensors is provided with, for example, an A/D converter for converting signals being read from the optical sensors into digital signals and a recognition processing portion for obtaining touch positions on the basis of the resultant digital signals. Consequently, the display device with optical sensors has a problem of its power consumption being higher than display devices without optical sensors.
Therefore, in one conceivable method for reducing power consumption, the display device with optical sensors has a normal mode and a standby mode set therefor, and in the standby mode, circuits can be stopped from operating, or their operation can be slowed, with the recognition processing portion being deactivated. In relation to this, Japanese Laid-Open Patent Publication No. 2006-201763 describes a display device having a photo-sensitive portion and a touch-sensitive portion provided on a display panel, in which, depending on a determination based on an output signal of the touch-sensitive portion, transition to the standby mode takes place when no contact has been made for a predetermined period of time, and transition to the normal mode takes place when some contact has been made.